Unfortunately, I’m not aware of any specific references to guide you in stamping or carving of fresh shotcrete for vertical surfaces. In many ways carving and stamping is a technique that requires more of an artistic flare that a finisher develops by hands-on experience. One key aspect is to minimize the working of the surface as much as possible to prevent tearing or delaminating the shotcrete surface layers. Carving or stamping when the concrete has reached an appropriate level of set (not too hard or soft) must also be judged by the experienced shotcrete finisher.